1. Field of the Invention
The present invention relates to microwave circuits. More specifically, the present invention relates to surfaces used to selectively pass and reflect microwave signals.
While the present invention is described herein with reference to a particular embodiment for an illustrative application, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teaching provided herein will recognize additional modifications, applications and embodiments within the scope thereof.
2. Description of the Related Art
Frequency selective surfaces selectively pass microwave signals. A microwave signal applied to a frequency selective surface will be either passed through the surface or reflected off of the surface depending upon the electrical characteristics of the frequency selective surface and the frequency of the applied signal.
Reflector antennas make use of frequency selective surfaces to provide dual or multiple frequency band operation. Frequency selective surfaces generally consist of arrays of elements such as squares, circles, Jerusalem crosses, concentric rings or double squares supported by a dielectric substrate.
Frequency selective surfaces are known to have several limitations. In order to provide low insertion losses and reflection losses, frequency selective surfaces must generally be fabricated with multiple layers. However, the characteristics of multiple layer frequency selective surfaces are typically dependent on the angle of incidence of the microwave signal. Thus, the pass band and reflection band of the frequency selective surface may vary with the incidence angle of the applied microwave signal.
In addition, multiple layer frequency selective surfaces are generally difficult and costly to manufacture. Also, a multiple layer frequency selective surface may be unacceptable for certain uses including spacecraft applications due to increased weight and volume.
There is therefore a recognized need in the art for a frequency selective surface with low insertion and reflection losses, stable pass band and reflection band characteristics at varying angles of incidence, light weight, low cost and low volume suitable for spacecraft systems and other applications requiring a high ratio of pass band and reflection band transmission to weight, volume and cost.